Polymer-matrix composites (PMCs), such as high-temperature polymer-matrix composites (HTPMCs), are used in the aircraft and aerospace industry for the weight reduction they offer when used as a substitute for metal components. However, exposure to high temperatures (e.g., 350 degrees Fahrenheit to 700 degrees Fahrenheit) can change the mechanical properties of the PMCs and HTPMCs and may cause oxidation of the PMCs and HTPMCs. For example, some HTPMCs have lifetimes of approximately between 1,000 hours and 3,000 hours at such elevated temperatures. In an attempt to extend the lifetime of PMCs and HTPMCs, barrier coatings or layers which prevent, reduce, or inhibit the permeation of a selected substrate with a gas, vapor, and/or chemical have been developed, such as ceramic-based coatings, for use with PMCs and HTPMCs. However, ceramic-based barrier coatings and metal-based barrier coatings have coefficients of thermal expansion (CTEs) that are sufficiently different from PMCs and HTPMCs and can cause strain mismatch between the ceramic-based barrier coating and the PMC or HTPMC substrate. Strain mismatch may cause the coating to crack or spall, thereby exposing the substrate to the environment, which may result in oxidation of the PMC or HTPMC. Furthermore, sufficiently different coefficients of thermal expansion between the coating and PMC/HTPMC may cause delamination of the coating from the PMC/HTPMC.
In addition, oxygen-barrier coatings for use with PMCs and HTPMCs may be affected by use at elevated temperatures in the 350-degree Fahrenheit to 700-degree Fahrenheit range for extended periods by cracking, spalling, delamination, and/or eroding.
There is a need in the art for barrier-coating structures and methods providing reduced delamination and improved protection of a PMC/HTPMC from oxidation.